A typical present-day nappy or diaper comprises an absorbent pad sandwiched normally between a permeable inner layer of spun-bonded fabric and an impermeable outer layer of polyethylene.
Responding to market demand, manufacturers of nappies/diapers now offer an anatomically contoured product, hence with pads shaped to fit a selected anatomical form. The method commonly adopted in this instance is one of forming the single pads on a drum that presents a plurality of peripheral aspirating pockets, each shaped to match the required anatomical form, and is fed at a point on the periphery with a stream of absorbent material. The absorbent material deposited in the pockets of the drum is compacted by a roller, at a point downstream.
The stream of absorbent material is a blend of cellulose pulp, or fluff pulp, into which granules of superabsorbent polymer (SAP) material are introduced either with or against the flow, homogeneously to a greater or lesser degree, according to requirements.
Nappies/diapers of more recent design also present a double thickness of absorbent padding: a first top layer, smaller, positioned on a larger second layer beneath.
In certain cases, the first layer needs also to be positioned further forward on the second layer by a greater or lesser distance in order to reinforce selected areas, depending on the gender or the age of the baby or on other factors.
Moreover, to improve the drainage of the absorbed liquid and simultaneously reduce production costs, manufacturers are opting for absorbent pads of which the composition is based on an increasingly greater quantity of SAP granules and a correspondingly smaller quantity of fluff pulp.
Adopting this new formulation, the need has also arisen for the absorbent pad to be more effectively compacted, since with a higher proportion of SAP material, which is of sand-like consistency, the structure tends to be less cohesive.
To meet the requirement for two layers of padding, the aforementioned drums present an aspirating pocket with an area of greater depth, contoured to match the shape of the finished pad. In this instance however, a special drum is needed for each relative position of the two layers, so that machines having a single drum offer scant versatility. The absorbent material can nonetheless be successfully compacted utilizing a drum of the type in question, creating a one-piece core that is easily handled and processed.
In an alternative solution, use is made of a first drum with peripheral aspirating pockets contoured to match the shape of the larger layer of padding, and a second drum adjacent to the first, set apart at a given distance, with aspirating pockets contoured to match the shape of the smaller top layer. Located beneath both of the drums is a belt conveyor, onto which the layers of absorbent material are released. The single layers are compacted by respective rollers operating between each drum and the conveyor. The larger layer is fed by the conveyor into the space beneath the second drum, from which the smaller layer is released onto the selfsame larger layer in a selected position. The timing of the two drums can be controlled in such a way as to vary the position in which the second layer is released onto the first layer. A drawback with this second solution, which envisages a first compression only of the first layer and a second compression of the second when paired with the first, is that the two layers cannot be compacted in such a way as to form a one-piece core, since the compression is applied in two successive stages, rather than simultaneously in a single step immediately before the absorbent pad is assembled with the other parts of the nappy/diaper.
The object of the present invention is to provide a unit for forming multilayer absorbent pads used in nappies/diapers, offering greater versatility than prior art units, and a method of forming such pads.
A further object of the invention is to provide a unit and a method for forming multilayer absorbent pads used in nappies/diapers whereby at least two layers of absorbent material can be suitably positioned and compacted simultaneously so as to produce a one-piece core, before the absorbent pad is assembled with the nappy/diaper pant.